A manufacturing process for an endless transmission belt on a flat bed knitting machine is described in German Patent DE-PS 12 84 734. Transmission and conveyor belts manufactured in this way cannot be used optimally everywhere, because the thread position of the weft thread, for example, unavoidably has a certain amount of waviness by reason of the insertion, necessary for production, of the weft thread in the form of a tuck loop. Because of this wave-shaped thread insertion the final belt length can be determined only empirically and cannot be exactly predetermined during production. For this reason it is necessary to prepare samples at the start of a production run in order to determine the exact belt length.
Another disadvantage of this fabric is its asymmetric structure. Because the fabric is produced as tubular goods, there always is a single-faced right/left knitting construction with side-by-side wales. These wales cause formation of ribs, especially with coarse fabrics made to an E8 or E6 gauge, i.e. six to eight needles/inch for heavy transmission belts, which result in development of considerable running noises when the belt is used at high speeds.
Because of the insertion of the weft thread in a tuck loop and the wave-shaped deformation of the thread caused thereby, it is difficult to maintain the thread insertion exactly the same across the fabric width as well as the thread insertion between the front needle bed and the rear needle bed. These different thread insertions cause differences in tension within the finished belt, which result in a considerable impairment of the straight running of the belt. But even the introduction of a double thread can only be done with great effort and with a loss of the quality of the finished endless belt. Multiple thread crossings are caused by the uncontrolled insertion of the double thread, which results in an erratic mesh pattern and, in particular, in differences in tension within the individual threads. This is particularly critical if it is intended to process materials of different yarn twists together in a known manner, for example left-hand twisted "S" and right-hand twisted "Z", to improve the straight running of the endless belt.
It is known that the yarn twist of a thread affects an endless belt in such a way that, when it runs over two parallel cylindrical disks it always runs in the respective direction of twist of the carrier thread. For this reason it is known to insert two threads in parallel. However, when employing two threads with S-twist and Z-twist, the insertion becomes uncontrolled in the normal right/left knitting construction with thread couliering and, as a result, there is frequent ride-over or twisting of the two threads. This naturally leads to an irregular final appearance of the goods and to thickening at the ride-over points.
It is known from German Patent DE-PS 88 324 to produce a right/right tubular fabric with weft threads on a flat bed knitting machine (FIGS. 1, 2). However, auxiliary needles and narrowing combs are needed for freeing a path for the weft thread. Since there is no needle division and all needles C.sub.1 always operate, it is necessary to transfer the loops of the auxiliary needles laterally to the needles C.sub.1.
It is further known to those skilled in the art that it is impossible to produce a symmetrical tubular fabric on a conventional flat bed knitting machine.
To produce a useful fabric and to achieve a somewhat efficient production, the machine should be equipped with electronic needle selection and at least three knitting systems connected one behind the other.